1. Field of the Invention
The invention relates to an automatic level control device for vehicles with air suspension based on which a vehicle chassis is spring-supported versus at least one vehicle axle.
2. Brief Description of the Background of the Invention Including Prior Art
Such an automatic level control device has been taught in the German Patent Application Laid Open DE-OS 3,031,453.
According to constructions of the conventional kind, the usually electrically actuatable shut-off valve or directional control valve, which valve usually is connected via a pressure line directly to the air spring, is formed as a seat valve such that the air pressure prevailing in the the air spring acts as a closure pressure on the seat valve. In this case, it is advantageously prevented that dynamically caused pressure changes could cause an unintended opening of the directional control valve based on a compression of the air spring.
This requires, however, that a force has to be furnished for the opening of the seat valve with the electrical actuation device. Said force has to overcome a maximum closure pressure, corresponding to a maximum air spring pressure in addition to the force of a usually present valve-closure spring. It is known in general that, in case of constructions of the precedingly mentioned kind, a quick response in case of automatic level controls can only be achieved by means of a corresponding passage capacity of the recited seat valve. The expansion of the passage cross-section of the seat valve, however, is limited as the force required for the opening of the seat valve also increases overproportionally with the expansion. This results in a disadvantageous way in relatively large device components of the electrical actuation device of the valve.